1. Field of the Invention
The present invention is directed to an arrangement for printing a print image, such as a postage meter machine, wherein different regions of the print image can be printed with respectively different resolutions.
2. Description of the Prior Art
U.S. Pat. No. 4,746,234 discloses a postage meter machine with a thermal transfer printer that allows the print image information to be easily changed. Semi-permanent and variable print image information is electronically stored as print data in a memory and read out into a thermal transfer-printing device for printing. This solution was employed in the commercial postage meter machine T1000 offered by Francotyp-Postalia AG and Co. KG and was the first time that an advertising imprint could be changed by pressing a button.
A method and an arrangement for internal cost center printing are available for department-by-department accounting of the value of postage fees consumed with the postage meter machine T1000, with a print image that is rotated by 90xc2x0 or 270xc2x0 being generated by means of a specific print controller (European Application 580 274, U.S. Pat. No. 5,790,768).
Printing business cards, fee stamps and court costs stamps is also possible with the T1000 machine, i.e. generating print images that differ considerably in structure and content from a franking imprint.
A franking imprint usually comprises a postal value stamp, a postmark image with the mail-receiving location and date as well as the aforementioned advertising image and is generated in the aforementioned sequence with, for example, the postage meter machine T1000 by means of printing print columns arranged perpendicular to the transport direction of the item being franked. The overall print column is imprinted by a single thermal transfer printhead. The machine can thus achieve a maximum throughput of franking matter of 2200 letters/hour with a print resolution of 240 dots per 30 mm, i.e. 203 dpi, but the manual feed of franking items limits the throughput of franking items that can be achieved in practice.
European Application 578 042 (corresponding to U.S. Pat. No. 5,608,636) discloses a method for controlling the column-by-column printing of a postage imprint, wherein encoded image information are converted before the printing event into binary signals for driving print elements, whereby the converted, variable and invariable image cannot be compiled until during printing. The decoding of the variable print data and offering of the print data for a complete column in a register ensue by means of a microprocessor. Since the data for the next print column must be edited in the time between two print columns, the computing time of the microprocessor must be in conformity with the proportion of variable print data, the level of franking items, throughput of franking items, and the print resolution. This increases the busload and limits the possibility of printing a franking imprint onto franking items faster. The franking imprint contains postal information including the postage fee data for delivering the letter. Modem postage meter machines enable a security imprint, i.e. an imprint of a specific marking in addition to the aforementioned information. For example, the aforementioned information is used to generate a message authentication code or a signature and a character string or a bar code as a marking. When a security imprint is printed with such a marking, this enables a review of the authenticity of the security imprint, for example in the post office or on the premises of a private carrier (U.S. Pat. Nos. 5,953,426 and 6,041,704).
In some countries, due to the development of postal requirements for a security imprint, the amount of variable print image data that must be modified between two imprints of different franking stamps is very high. For Canada, for example, a data matrix code of 48xc3x9748 picture elements must be generated and printed for every individual franking imprint.
An ink jet printhead can be composed of a number of modules according to the xe2x80x9cnon-interlacedxe2x80x9d principle when the spacings between the nozzles are too large and the number of nozzles of a module are inadequate for printing a printing width of 1 inch (=25.4 mm) with one module given a resolution of approximately 200 dpi. In the ink printhead of the commercial postage meter machine JetMail(copyright), for example, three modules are arranged offset from one another in the column direction of the print image. Each module has only one row of nozzles with 64 nozzles and the modules are arranged slanted to such an extent relative to the print column so that each nozzle row describes an acute angle relative to the transport direction of the materials to be franked. The individual nozzles of each module therefore do not print along a print image column but print along a diagonal that intersects the columns of the print image. As a consequence, pixel offset errors accumulate when the transport velocity is not correctly acquired. Despite acquiring the movement of the franking matter in the transport direction with a high-quality encoder, it is difficult to print a line straight in the direction of the print image column. The individual modules and their offset from one another, moreover exhibit tolerances that arise in the manufacture of the modules. Below a size that is spaced one print image column from the next, a print pulse is supplied with different delay for each module.
A method and an arrangement for tolerance compensation are described in European Applications 921 008 and 921 009, wherein individual printhead data are stored in a non-volatile memory of the printhead and taken into consideration in the print pulse delay. When the pixel offset error exceeds the size by which a print column is spaced from the next, then the binary pixel data in the pixel memory must be changed.
A solution for print image generation for the JetMail(copyright) disclosed by U.S. Pat. No. 5,707,158 and European Application 762 334 describes how the data describing a complete print image are generated and stored before the printing, and is based on a control datafile for field-by-field generation of the print image in a pixel memory before the printing. The print image is defined in image sub-datafiles of the control datafile and is stored as pattern in pixel datafiles. So that the printer device can directly access the pixel data, binary pixel data are not stored in a pixel memory in the sequence along a print image column but are stored as a modified pattern along a diagonal in three sub-regions lying above one another in order to compensate changes in the pattern caused due to the non-interlaced arrangement of the modules. The solution is based on complete patterns of binary pixel data modified dependent on a pixel data change unit, the binary pixel data being intermediately stored in the pixel memory. The print images are compiled before the printing such that the images are read by a print data controller directly from the pixel memory into a shift register, and are serially transmitted to a shift register in the printhead and can be transferred into a latch. The print data controller is realized together with other assemblies in an ASIC (U.S. Pat. No. 5,710,721, European Application 1 154 382).
Some postal demands can be satisfied only with this solution since the microprocessor is supported by the specific pixel data change unit in the ASIC on the Jet Mail CPU board when modifying the image data of variable picture elements. The pixel data change unit is capable of modifying the variable picture elements between successive frankings such that these are stored in the form of binary pixel data in a pixel memory before the printing. The arrangement of the picture elements (pixels) in the pixel memory required for the printing is not beneficial for the modification of picture elements by the microprocessor because of the oblique position of the print modules of the printhead, and would require a high computing outlay. Even given support by a pixel-editing unit, this can only modify a small number of variable picture elements between the imprints.
U.S. Pat. No. 5,651,103 discloses an apparatus and a method for column-by-column printing of an image in real time, wherein variable and fixed image data elements are connected to one another and deposited in a buffer in order to then be used for printing a column. The variable and fixed image data elements are stored in a non-volatile memory, with some of the fixed image data elements being compressed. The print image data for printing each print column are compiled from variable and invariable image data only before they are printed, i.e. the image data for an imprint are not present in binary form in a memory area but in a form that is comparable to the method disclosed by European Application 578 042 for the T1000. The variable image data elements in the non-volatile memory are identified by a controller, and data that correspond to the variable image data elements are transferred to a further controller in order to download the variable and fixed image data elements, unite them with one another, and then print them. The controller proposed for this requires a variable address register for each variable image data element. The number of variable image data thus is limited by the number of address registers.
A postal half-inch ink jet printhead with bubble-jet technology is currently employed in some postage meter machines, this being arranged in a cartridge of, for example, the type HP 51640 of Hewlett Packard and being protected by special means (European Application 1 132 868). 300 nozzles are arranged in two nozzle rows in the half-inch ink jet printhead, these being arranged orthogonally relative to the transport direction of the franking matter and arranged offset relative to one another in the column direction of the print image and in the transport direction of the franking matter (xe2x80x9cinterlacedxe2x80x9d principle).
European Application 1 176 016 A2 discloses ink jet printheads that are specifically protected and drivable for a franking imprint in greater detail. In order to print a franking imprint having a print column length of 1 inch=25.4 mm and having a maximum resolution of up to 600 dpi in the print image column direction with a postage meter machine in one pass of the franking item, two half-inch ink jet printheads are arranged offset relative to one another in the print image column direction and in the transport direction of the franking item. The print image is generated from the print image columns in this orthogonal arrangement relative to the transport direction of the franking matter, with each of the printheads printing a part of the print image column. The machine thus can achieve a high throughput of franking items (5500 letters an hour). The quantity of print image data that must be modified between two imprints is not only very large but also must be made available in a shorter time. When, however, the storing of the binary print image data in the pixel memory for the pixels ensues in the specific sequence in which the pixel data are required for the drive of the two postal half-inch ink jet printheads with bubble-jet technology when printing a column, then the print image is mapped in the pixel memory as a correspondingly modified pattern of binary pixel data. The modification of picture elements by the microprocessor thus becomes complicated again and requires a high computing outlay that can be achieved in the required time only by means of an expensive microprocessor, or the throughout of franking matter is correspondingly reduced.
An object of the present invention is to provide an economical solution for the control of printing a print image having regions with different print image resolution on moving postal items in a mail processing device with high-resolution printheads for a high throughput of postal items. With simple intermediate storing and address calculation before the printout, the microprocessor responsible for the control of a complete mail processing system should be relieved.
The above object is achieved in accordance with the principles of the present invention in an arrangement for printing a print image wherein the pixel data, representing an image to printed, are arranged in data words grouped in data strings and are stored in compressed form. A print data controller has access to the memory wherein the print data are stored, and edits the print data and supplies the edited print data to a printer for printing the image. A microprocessor, which controls the overall operation of the printer arrangement, supplies a signal to the print data controller which determines a degree to decompression of the compressed data, this degree of decompression being determinative of the resolution of the printing which will take place using the decompressed pixel data. The image is printed column-by-column, and thus for columns representing a particular region of the print image, the decompression factor, and thus the amount of supplemental data which must be generated by the print data controller in the decompression process, is selected dependent on the desired resolution for that region of the image.
The inventive solution is based on the ink jet printheads that are employed meeting high demands as to the print resolution. The print resolution of a print image column disposed orthogonally to the transport direction of a piece of mail can reach a maximum value (600 dpi). The mail-processing device is, for example, a postage meter machine that prints a franking stamp as the print image with a predetermined number of print image columns approximately one inch long. A commercially available ink jet printhead having a half-inch width can only print out a part of the print image (print half-frame), so two such half-inch ink jet printheads are required for printing an entire print image. An image in the form of a pattern of binary pixel data exists for each part of the print image to be printed out by the respective ink jet printheads. The pixel data for two complete print half-frames are generated by the microprocessor using data from a read-only memory and are stored in the pixel memory in the form of data words. The number of data words in a data string corresponds to the maximally possible print resolution of the printhead. The binary pixel data stored in the pixel memory are transmitted to the print data controller and grouped corresponding to the type of printhead during printing. The print image, however, may contain sections that need not be printed with high resolution. Since a pattern with a number of data strings arranged in columns represents the print image, a representation of a compressed print image section arises when the binary pixel data are stored compressed in data words of a data string. The fact that the length of the data strings that arise is reduced contributes to a considerable saving of memory space in the pixel memory. The missing pixel data are generated by the print data controller upon decompression of the data. Pixel data are stored by words in the pixel memory in an easily modified and binary form, and a switchable number of data words are provided for printing sections in the print image with modified resolution, and the print data controller is correspondingly fashioned to be switchable dependent on the modified print image resolution.
The print data controller generates a print image dependent on the required resolution and thus relieves the microprocessor utilized in the mail processing device of the task of modifying the print data of the variable print image elements in the pixel memory between frankings. Subsequently or parallel thereto, print data are transferred to the print data controller by direct memory access (DMA). Since the microprocessor is also responsible for the complete control of the entire mail processing system, additional control functions are also realized, for instance the regulation of the transport motor for postal matter and the control of the closer device and feeder device and possibly other peripheral devices. The demands made on such a processor that is employed, which for const reasons cannot be a complicated, high capacity processor, are therefore very high and lead to a high workload for its limited computing capacity.
The modification of picture elements is simplified, which produces a lower computing outlay for the microprocessor by the half-frame to be printed by the respective printhead being represented in the pixel memory in the form of binary pixel data so that an optimally large amounts of binary pixel data of a picture element can be modified with each command of the microprocessor. This allows according to the invention, the use of a print data controller that undertakes pixel data editing for each printhead. Two pixel data-editing units are driven by a specific controller in order to transfer binary pixel data from the pixel memory into a buffer memory and in order to select binary pixel data bit-by-bit. The selected pixel data are written into a collecting register of the respective pixel data editor and are subsequently transferred into a shift register, so that the pixel data are supplied in a specific sequence from the shift register that is required when printing print columns with the two postal half-inch ink jet printheads. The microprocessor is programmed to store a number of data strings with a switchable number of data words in the pixel memory. The print data controller is equipped to supplement pixel data missing because of the compression such that the reduction in the number of data words per data string corresponds to the reduction of the resolution during printing.
The specific controller in the print data controller includes a DMA control unit, an address generator and a printer controller. The DMA control unit is switchable for generating a print image with low resolution, so that the number of DMA cycles is at least halved when loading binary pixel data into the buffer memories. The address generator, which is likewise switchable, then generates at least halved read addresses for a read access onto the buffer memories.
The printer controller is connected to an encoder that supplies a pulse rate corresponding to the transport velocity of the postal items. The printer controller is equipped to initiate the loading of a data string with the binary pixel data for one of the print columns into a buffer memory, and increments and evaluates a count value of a data string counter. When the content of this data string counter is equal to the content of a reference value register, the printer controller outputs an FD signal corresponding to the current print resolution. A control line via which at least one FD signal having a value of xe2x80x9conexe2x80x9d can be transmitted is present at the control input of the DMA controller. When such an FD signal with the value xe2x80x9conexe2x80x9d is present, then the DMA controller is initiated to execute a maximum number of cycles for loading data words with binary pixel data for a maximum resolution. Half the number of data words thereof is loaded into each buffer memory, provided for each half-inch printhead. The address generated by the address generator is then employed for reading out pixel data from the buffer memory. When, however, an FD signal with an alternative value is present at the control input of the DMA controller via the control line, then the DMA controller is initiated to execute fewer than the maximum number of cycles for loading data words with binary pixel data for a reduced resolution. The ratio of the maximum number of DMA cycles to the reduced number of DMA cycles corresponds to the compression factor FD communicated via the FD signal, with the compression factor FD applied to the data string being equal to the decompression factor FA communicated to the address generator via the FA signal. If further reference value registers are present, the current print resolution is modified with every further equality of the reference value of one of the reference value registers with the current count value of the data string counter. Printing is ended when the data string counter has reached a prescribed limit value.
Advantages with respect to the calculating time are achieved for the microprocessor and advantages with respect to the need for memory space are achieved for the pixel memory as a result of the print data controller.
Since the microprocessor must execute fewer cycles for loading a data string into the buffer memories in the print image regions with low resolution, the busload is reduced and the microprocessor has more time available for program processing.
Because of the modification of variable print image elements, fewer data need to be modified by the microprocessor between the frankings. The required calculating time is reduced as a result.
Since the number of data words per data string is reduced by print image sections with low resolution, smaller memory modules can be employed for storing a larger dataset, or some memory modules possibly can be eliminated, which reduces the manufacturing costs.